Semiconductor devices having tensile and/or compressive stress and methods of manufacturing

ABSTRACT

Semiconductor devices are provided which have a tensile and/or compressive strain applied thereto and methods of manufacturing. A method of forming a semiconductor structure includes forming sidewalls and spacers adjacent to a gate stack structure, and forming a recess in the gate stack structure. The method further includes epitaxially growing a straining material on a polysilicon layer of the gate stack structure, and in the recess in the gate stack structure. The straining material is Si:C and the gate stack structure is a PFET gate stack structure. The straining material is grown above and covering a top surface of the sidewalls and the spacers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application to U.S.application Ser. No. 12/047,376, filed on Mar. 13, 2008, the contents ofall of which are herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to semiconductor devices andmethods of manufacturing the same, and more specifically, tosemiconductor devices having a tensile and/or compressive strain appliedthereto and methods of manufacturing.

BACKGROUND OF THE INVENTION

Mechanical strains within a semiconductor device substrate can modulatedevice performance by, for example, increasing the mobility of thecarriers in the semiconductor device. That is, strains within asemiconductor device are known to enhance semiconductor devicecharacteristics. Thus, to improve the characteristics of a semiconductordevice, tensile and/or compressive strains are created in the channel ofthe n-type devices (e.g., NFETs) and/or p-type devices (e.g., PFETs),respectively. However, the same strain component, for example tensilestrain or compressive strain, improves the device characteristics of onetype of device (i.e., n-type device or p-type device) whilediscriminatively affecting the characteristics of the other type device.

Accordingly, in order to maximize the performance of both NFETs andPFETs within integrated circuit (IC) devices, the strain componentsshould be engineered and applied differently for NFETs and PFETs. Thatis, because the type of strain which is beneficial for the performanceof an NFET is generally disadvantageous for the performance of the PFET.More particularly, when a device is in tension (in the direction ofcurrent flow in a planar device), the performance characteristics of theNFET are enhanced while the performance characteristics of the PFET arediminished.

To selectively create tensile strain in an NFET and compressive strainin a PFET, distinctive processes and different combinations of materialsare used. For example, liners on gate sidewalls have been proposed toselectively induce the appropriate strain in the channels of the FETdevices. By providing liners the appropriate strain is applied closer tothe device. While this method does provide tensile strains to the NFETdevice and compressive strains along the longitudinal direction of thePFET device, they may require additional materials and/or more complexprocessing, and thus, result in higher cost. Further, the level ofstrain that can be applied in these situations is typically moderate(i.e., on the order of 100s of MPa). Thus, it is desired to provide morecost-effective and simplified methods for creating larger tensile andcompressive strains in the channels of the NFETs and PFETs,respectively.

Accordingly, there exists a need in the art to overcome the deficienciesand limitations described hereinabove.

SUMMARY OF THE INVENTION

In a first aspect of the invention, a method of forming a semiconductorstructure comprises epitaxially growing a straining material on apolysilicon layer of a gate stack structure.

In an additional aspect of the invention, a semiconductor structurecomprises an epitaxially grown straining material on a polysilicon layerof a gate stack structure.

In a further aspect of the invention, a structure comprises a gate stackcomprising an oxide layer, a polysilicon layer and sidewalls withadjacent spacers. The structure further comprises an epitaxially grownstraining material directly on the polysilicon layer and betweenportions of the sidewalls. The epitaxially grown straining materialstrains the polysilicon layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIGS. 1-8 show structures and respective processing steps for forming astrained device in accordance with aspects of the invention; and

FIGS. 9-19 show structures and respective processing steps for forming astrained device in accordance with another aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to semiconductor devices having tensileand/or compressive strains and methods of manufacturing. By implementingthe invention, it is possible to increase electron mobility enhancementunder a gate to increase device performance, regardless of the scale ofthe device. More specifically, the invention is directed tosemiconductor devices and methods of manufacture which provide tensilestrains near the NFET channel and compressive strains near the PFETchannel of CMOS devices. In implementation, the present invention canintegrate SiGe and Si:C materials into CMOS technology.

Advantageously, the present invention provides a device that, inembodiments, forms a straining cap layer directly on a polysilicon layerof a gate structure. The straining cap layer can be epitaxially grownSiGe or Si:C materials. When epitaxially grown directly on the polylayer of the gate, the SiGe or Si:C layer will have a lattice constantthat conforms to that of the underlying polysilicon layer. Uponrelaxation, the SiGe lattice constant approaches that of its intrinsiclattice constant which is larger than that of the polysilicon which, inturn, applies physical biaxial strain (e.g., expansion) to theunderlying polysilicon layer. This physical strain forms a tensilestrain which is beneficial to an N type device performance.

In the case of Si:C, for example, upon relaxation, the lattice constantapproaches that of its intrinsic lattice constant which is smaller thanthat of the underlying polysilicon layer. This, in turn, appliesphysical biaxial strain (e.g., contraction) to the underlyingpolysilicon layer. This physical strain forms a compressive strain whichis beneficial to P type device performance. In further embodiments, anSiGe material may be provided on sides of a P type device to furtherimprove the performance of such device.

First and Second Aspects of the Invention

FIG. 1 shows a starting structure and respective processing steps forforming a FET in accordance with the invention. The starting structureincludes, for example, a gate oxide layer 12 deposited over an activearea of a wafer 10 in a conventional deposition process. In oneillustrative embodiment, the gate oxide layer 12 can have a thicknessranging from about 10 Å to 20 Å. Although not shown in FIG. 1, it shouldbe understood that shallow trench isolation (STI) structures can beprovided on sides of the active region of the wafer 10. The wafer 10 canbe any known type of wafer used with the formation of FETs. For example,the wafer 10 can be silicon, BULK, SOI, SiGe or Gallium arsenic, to namea few.

FIG. 2 shows a conventional gate stack deposition process such as, forexample, using chemical vapor deposition processes. In particular, apolysilicon material 14 is deposited on the gate oxide layer 12 and aSiGe material 16 is deposited on the polysilicon material 14. Inembodiments, the SiGe material is preferred as it can be removed moreeasily in later processing steps. In embodiments, the gate stack isabout 100 nm. In all aspects of the invention, though, it should beunderstood that the size and location of the gate stack can be varieddepending on the technology application.

FIGS. 3 and 4 show intermediate structures and respective processingsteps in accordance with the invention. More specifically, in FIG. 3, aresist R is deposited on the structure of FIG. 2 and patterned usingconventional lithographic processes. By way of illustration, a resist isplaced over the structure of FIG. 2 and selective portions of the resistare exposed to form openings. In subsequent processes as shown in FIG.4, the gate oxide layer 12, polysilicon material 14 and SiGe material 16are patterned to form a gate stack, generally represented at referencenumeral 18.

FIG. 5 shows the formation of sidewalls and spacers using conventionalprocesses. The sidewalls and spacers are represented generally byreference numeral 20. In embodiments, the sidewalls are oxide formedduring an oxidation process and the spacers are silicon nitride (Si₃N₄).After the formation of the spacers, a RIE process is used to form thestructure 20 shown in FIG. 5. As the formation of the sidewalls andspacers are known to those of skill in the art, a more detailedexplanation of such formation is not necessary for the understanding ofthe invention.

FIG. 6 shows an intermediate structure and respective processing stepsin accordance with the invention. More specifically, in FIG. 6, the SiGematerial is removed in a conventional selective etching process to forma recess 22 in the gate stack. For example, using either a wet etchingor dry etching process, the SiGe material is removed from the gatestructure to form the recess 22.

FIG. 7 shows a top view of a final structure and respective processingsteps in accordance with the invention. FIG. 8 shows a cross-sectionalview of FIG. 7 along lines A-A. As shown in FIGS. 7 and 8, anepitaxially grown strain material 24 is grown in the recess 22 of FIG.6. The strain material 24 can extend above the structure to a height ofabout 30 nm to 50 nm; although, in embodiments, the strain material 24is preferably planar or substantially planar with the surface of thestructure. In embodiments, the strain material 24 can be SiGe to providea tensile strain for an NFET device. Alternatively, the strain material24 can be Si:C to provide a compressive strain for a PFET device.

As should be understood by those of skill in the art, the SiGe materialwill provide a tensile stress in the channel of the NFET. Morespecifically, to increase the strain levels in a NFET device, theepitaxially grown SiGe layer, in an unrelaxed state, will have a latticeconstant that conforms to that of the underlying polysilicon layer. Uponrelaxation (e.g., through a high temperature process for example), theSiGe lattice constant approaches that of its intrinsic lattice constantwhich is larger than that of the underlying polysilicon layer.Accordingly, the underlying polysilicon layer conforms to the largerlattice constant of the relaxed SiGe layer which results in a physicalbiaxial strain (e.g., expansion) to the polysilicon layer. This physicalstrain applied to the polysilicon layer is beneficial because theexpanded polysilicon layer increases N type device performance.

Also, as should be understood by those of skill in the art, the Si:Cmaterial will provide a compressive strain in the channel of the PFET.More specifically, to increase the strain levels in a PFET device, theepitaxially grown Si:C layer, in an unrelaxed state, will have a latticeconstant that conforms to that of the underlying polysilicon layer. Uponrelaxation (e.g., through a high temperature process for example), theSi:C lattice constant approaches that of its intrinsic lattice constantwhich is smaller than that of the underlying polysilicon layer.Accordingly, the polysilicon layer conforms to the smaller latticeconstant of the relaxed Si:C layer which results in a physical biaxialstrain (e.g., contraction) to the polysilicon layer. This physicalstrain applied to the polysilicon layer is beneficial because thecontracted polysilicon layer increases P type device performance.

Third Aspect of the Invention

FIG. 9 shows a starting structure in accordance with another aspect ofthe invention. More particularly, the starting structure of FIG. 9includes a beginning structure for an NFET and PFET, isolated from oneanother by an STI structure. The beginning structures for the NFET andPFET are fabricated according to the processes shown in FIGS. 1-5.

More specifically, the STI structure is formed in a conventional mannerusing photolithographic and etching processes to form a trench. Thetrench is then filled with an oxide, for example. As to the NFET andPFET structures, a gate oxide layer 12 is deposited over an active areaof a wafer 10 in a conventional deposition process (as discussed withreference to FIG. 1). A polysilicon 14 and an SiGe material 16, forexample, are deposited over the gate oxide layer 12. A gate stack isthen patterned in accordance with the processes shown, for example, inFIGS. 2-4. Sidewalls and spacers 20 are formed using conventionalprocesses as described with reference to FIG. 5.

As shown in FIG. 10. a resist 26 is formed over the NFET of FIG. 9.Thereafter, as shown in FIG. 11, an etching process will remove the SiGelayer of the PFET to form a recess 28, as the resist 26 protects theNFET side of the device. The resist 26 is stripped away using aconventional stripping process.

As shown in FIG. 12, an oxide 30 is formed over the structure of FIG.11. The oxide 30 can be formed using any conventional oxidation process.As shown in FIG. 13, the oxide is planarized using a conventionalchemical mechanical polishing process. As shown in FIG. 13, oxide 30remains within the recess 28 of the PFET.

FIG. 14 shows an intermediate structure and respective processing stepsin accordance with the invention. More specifically, in FIG. 14, aresist 32 is formed over the NFET structure. An etching process, e.g.,SiO₂ Reactive Ion Etching (RIE), removes the oxide layer on the waferand sidewall structure of the PFET.

As shown in FIG. 15, recesses 36 are formed in the wafer, e.g.,substrate, using a conventional RIE process. The recesses 36 are formedin the source/drain regions of the PFET. During this processing, theNFET structure remains protected by a resist.

In FIG. 16, the resist and the SiGe layer on the NFET stack are removedusing a conventional stripping and etching processes known to those ofskill in the art. In further fabrication processes, a SiGe material 38is epitaxially grown in the recess of the NFET stack and the recesses36. As discussed above, the epitaxially grown SiGe will create tensileand compressive strains in the channels of the NFET and PFET,respectively.

FIG. 17 shows the removal of the remaining oxide layer about the NFETand on the polysilicon 14 of the PFET stack. The removal of the oxidelayer on the PFET stack results in a recess 40.

As representatively shown in FIG. 18, a silicidation process isperformed, e.g., a high temperature anneal, over the structure of FIG.17 to form silicide 42. In embodiments, the silicide 42 is formed in thesource and drain regions of the NFET and the PFET. In addition, thesilicide 42 is formed on the NFET and PFET stacks.

In FIG. 19, the silicide and SiGe layer are removed from the NFET stackto form a recess (not shown), and the silicide layer is removed from thePFET stack. An epitaxially grown strain material 24 is provided in therecess formed in the NFET stack (similar to that shown in FIGS. 7 and8). As disclosed above, the strain material 24 can extend above thestructure; although, in embodiments, the strain material 24 ispreferably planar or substantially planar with the surface of thestructure. In embodiments, the strain material 24 can be an SiGematerial to provide a tensile strain for an NFET device (in the mannerdisclosed above). An oxide cap 44 is formed on the remaining portion ofthe PFET stack in a conventional manner, which should be known to thoseof skill in the art.

The methods as described above are used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

While the invention has been described in terms of embodiments, those ofskill in the art will recognize that the invention can be practiced withmodifications and in the spirit and scope of the appended claims.

What is claimed is:
 1. A method of forming a semiconductor structurecomprising: forming sidewalls and spacers adjacent to a gate stackstructure; forming a recess in the gate stack structure; epitaxiallygrowing a straining material on a polysilicon layer of the gate stackstructure, and in the recess in the gate stack structure; and relaxingthe epitaxially-grown straining material such that a lattice constant ofthe straining material is an intrinsic lattice constant of Si:C that issmaller than a lattice constant of the polysilicon layer, wherein thestraining material is Si:C and the gate stack structure is a PFET gatestack structure, wherein the straining material is grown above andcovering a top surface of the sidewalls and the spacers, and wherein themethod further comprises: forming a gate oxide layer on a wafer of thesemiconductor structure; forming the polysilicon layer on the gate oxidelayer; and forming a SiGe layer on the polysilicon layer.
 2. The methodof claim 1, further comprising patterning the gate oxide layer, thepolysilicon layer, and the SiGe layer to form the gate stack structure.3. The method of claim 2, further comprising removing the SiGe layerfrom the gate stack structure to form the recess in the gate stackstructure.
 4. The method of claim 1, further comprising: forming aresist on the SiGe layer; and exposing one or more selective portions ofthe resist to form one or more openings in the resist.
 5. The method ofclaim 4, further comprising patterning the gate oxide layer, thepolysilicon layer, and the SiGe layer to form the gate stack structurebased on the one or more openings.
 6. The method of claim 1, wherein:the sidewalls are oxide; and the spacers are silicon nitride.
 7. Themethod of claim 1, wherein the straining material is substantiallyplanar above a surface of the semiconductor structure.
 8. The method ofclaim 7, wherein the straining material extends laterally over and abovethe sidewalls and the spacers.
 9. A method of forming a semiconductorstructure comprising: forming sidewalls and spacers adjacent to a gatestack structure; forming a recess in the gate stack structure;epitaxially growing a straining material on a polysilicon layer of thegate stack structure, and in the recess in the gate stack structure; andrelaxing the epitaxially-grown straining material such that a latticeconstant of the straining material is an intrinsic lattice constant ofSi:C that is smaller than a lattice constant of the polysilicon layer,wherein the straining material is Si:C and the gate stack structure is aPFET gate stack structure, wherein the straining material is grown aboveand covering a top surface of the sidewalls and the spacers, and whereinthe method further comprises: forming second sidewalls and secondspacers adjacent to a second gate stack structure; forming a recess inthe second gate stack structure; epitaxially growing a second strainingmaterial on a polysilicon layer of the second gate stack structure, andin the recess in the second gate stack structure; and relaxing thesecond straining material such that an intrinsic lattice constant of thesecond straining material is larger than a lattice constant of thepolysilicon layer of the second gate stack structure, wherein the secondstraining material is SiGe and the second gate stack structure is anNFET gate stack structure.